[Sync] Refactor AttachmentStore classes. Introduce concept of referrer.

sync/internal_api/attachments/attachment_store_frontend.cc

-// Copyright 2014 The Chromium Authors. All rights reserved.
+// Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "sync/internal_api/public/attachments/attachment_store_handle.h"
+#include "sync/internal_api/public/attachments/attachment_store_frontend.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/sequenced_task_runner.h"
 #include "sync/api/attachments/attachment.h"
+#include "sync/api/attachments/attachment_store_backend.h"
 
 namespace syncer {
 
 namespace {
 
-// NoOp is needed to bind base::Passed(backend) in AttachmentStoreHandle dtor.
+// NoOp is needed to bind base::Passed(backend) in AttachmentStoreFrontend dtor.
 // It doesn't need to do anything.
 void NoOp(scoped_ptr<AttachmentStoreBackend> backend) {
 }
 
 }  // namespace
 
-AttachmentStoreHandle::AttachmentStoreHandle(
+AttachmentStoreFrontend::AttachmentStoreFrontend(
     scoped_ptr<AttachmentStoreBackend> backend,
     const scoped_refptr<base::SequencedTaskRunner>& backend_task_runner)
     : backend_(backend.Pass()), backend_task_runner_(backend_task_runner) {
   DCHECK(backend_);
   DCHECK(backend_task_runner_.get());
 }
 
-AttachmentStoreHandle::~AttachmentStoreHandle() {
+AttachmentStoreFrontend::~AttachmentStoreFrontend() {
   DCHECK(backend_);
   // To delete backend post task that doesn't do anything, but binds backend
   // through base::Passed. This way backend will be deleted regardless whether
   // task runs or not.
-  backend_task_runner_->PostTask(
-      FROM_HERE, base::Bind(&NoOp, base::Passed(&backend_)));
+  backend_task_runner_->PostTask(FROM_HERE,
+                                 base::Bind(&NoOp, base::Passed(&backend_)));
 }
 
-void AttachmentStoreHandle::Init(const InitCallback& callback) {
+void AttachmentStoreFrontend::Init(
+    const AttachmentStore::InitCallback& callback) {
   DCHECK(CalledOnValidThread());
   backend_task_runner_->PostTask(
       FROM_HERE, base::Bind(&AttachmentStoreBackend::Init,
                             base::Unretained(backend_.get()), callback));
 }
 
-void AttachmentStoreHandle::Read(const AttachmentIdList& ids,
-                                 const ReadCallback& callback) {
+void AttachmentStoreFrontend::Read(
+    const AttachmentIdList& ids,
+    const AttachmentStore::ReadCallback& callback) {
   DCHECK(CalledOnValidThread());
   backend_task_runner_->PostTask(
       FROM_HERE, base::Bind(&AttachmentStoreBackend::Read,
                             base::Unretained(backend_.get()), ids, callback));
 }
 
-void AttachmentStoreHandle::Write(const AttachmentList& attachments,
-                                  const WriteCallback& callback) {
+void AttachmentStoreFrontend::Write(
+    AttachmentStore::AttachmentReferrer referrer,
+    const AttachmentList& attachments,
+    const AttachmentStore::WriteCallback& callback) {
+  DCHECK(CalledOnValidThread());
+  backend_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&AttachmentStoreBackend::Write,
+                            base::Unretained(backend_.get()), referrer,
+                            attachments, callback));
+}
+
+void AttachmentStoreFrontend::Drop(
+    AttachmentStore::AttachmentReferrer referrer,
+    const AttachmentIdList& ids,
+    const AttachmentStore::DropCallback& callback) {
   DCHECK(CalledOnValidThread());
   backend_task_runner_->PostTask(
       FROM_HERE,
-      base::Bind(&AttachmentStoreBackend::Write,
-                 base::Unretained(backend_.get()), attachments, callback));
+      base::Bind(&AttachmentStoreBackend::Drop,
+                 base::Unretained(backend_.get()), referrer, ids, callback));
 }
 
-void AttachmentStoreHandle::Drop(const AttachmentIdList& ids,
-                                 const DropCallback& callback) {
-  DCHECK(CalledOnValidThread());
-  backend_task_runner_->PostTask(
-      FROM_HERE, base::Bind(&AttachmentStoreBackend::Drop,
-                            base::Unretained(backend_.get()), ids, callback));
-}
-
-void AttachmentStoreHandle::ReadMetadata(const AttachmentIdList& ids,
-                                         const ReadMetadataCallback& callback) {
+void AttachmentStoreFrontend::ReadMetadata(
+    const AttachmentIdList& ids,
+    const AttachmentStore::ReadMetadataCallback& callback) {
   DCHECK(CalledOnValidThread());
   backend_task_runner_->PostTask(
       FROM_HERE, base::Bind(&AttachmentStoreBackend::ReadMetadata,
                             base::Unretained(backend_.get()), ids, callback));
 }
 
-void AttachmentStoreHandle::ReadAllMetadata(
-    const ReadMetadataCallback& callback) {
+void AttachmentStoreFrontend::ReadAllMetadata(
+    AttachmentStore::AttachmentReferrer referrer,
+    const AttachmentStore::ReadMetadataCallback& callback) {
   DCHECK(CalledOnValidThread());
   backend_task_runner_->PostTask(
-      FROM_HERE, base::Bind(&AttachmentStoreBackend::ReadAllMetadata,
-                            base::Unretained(backend_.get()), callback));
+      FROM_HERE,
+      base::Bind(&AttachmentStoreBackend::ReadAllMetadata,
+                 base::Unretained(backend_.get()), referrer, callback));
 }
 
 }  // namespace syncer